AvaloniaUI/Avalonia · error · InvalidOperationException

Invalid size returned for Measure.

Error message

Invalid size returned for Measure.

What it means

Measure throws after MeasureCore returns a Size whose Width or Height is negative or non-finite (NaN/Infinity). This is the contract check on the OUTPUT of measure: subclasses overriding MeasureCore must return a valid, non-negative, finite desired size. Infinity or NaN in DesiredSize would corrupt every parent's measure math.

Source

Thrown at src/Avalonia.Base/Layout/Layoutable.cs:396

                var previousDesiredSize = DesiredSize;
                var desiredSize = default(Size);

                IsMeasureValid = true;

                try
                {
                    _measuring = true;
                    desiredSize = MeasureCore(availableSize);
                }
                finally
                {
                    _measuring = false;
                }

                if (IsInvalidSize(desiredSize))
                {
                    throw new InvalidOperationException("Invalid size returned for Measure.");
                }

                DesiredSize = desiredSize;
                _previousMeasure = availableSize;

                Logger.TryGet(LogEventLevel.Verbose, LogArea.Layout)?.Log(this, "Measure requested {DesiredSize}", DesiredSize);

                if (DesiredSize != previousDesiredSize)
                {
                    this.GetVisualParent<Layoutable>()?.ChildDesiredSizeChanged(this);
                }
            }
        }

        /// <summary>
        /// Arranges the control and its children.
        /// </summary>
        /// <param name="rect">The control's new bounds.</param>

View on GitHub (pinned to 11c5427268)

Solutions

1. In the MeasureCore/MeasureOverride override, ensure the returned Size has non-negative, finite Width and Height.
2. Clamp computed values: Math.Max(0, value) and guard against NaN/Infinity before returning.
3. If a child measure failed, fall back to a sensible default size rather than propagating an invalid result.

Example fix

// before
protected override Size MeasureCore(Size availableSize)
{
    return new Size(DesiredSize.Width / someDivisorThatIsZero, height);
}

// after
protected override Size MeasureCore(Size availableSize)
{
    var w = someDivisor != 0 ? DesiredSize.Width / someDivisor : 0;
    return new Size(Math.Max(0, w), height);
}

// Inside a MeasureCore/MeasureOverride override, validate the return value:
static Size Valid(Size s) => new Size(
    double.IsNaN(s.Width) || s.Width < 0 ? 0 : s.Width,
    double.IsNaN(s.Height) || s.Height < 0 ? 0 : s.Height);

return Valid(computedDesiredSize);

When it happens

Trigger: A custom Layoutable subclass whose MeasureCore override returns a Size with a negative component, NaN, or Infinity. Can also indicate arithmetic in the override that divided by zero or returned an uninitialized Size.

Common situations: Writing a custom control/panel and returning `new Size(double.NaN, ...)` or a negative value from MeasureCore/MeasureOverride. Forgetting to clamp a computed desired size. Returning DesiredSize before it was set.

Related errors

• Cannot call Measure using a size with NaN values.
• The control isn't currently attached to a toplevel
• Invalid render scaling value {scaling}
• Attempt to call InvalidateMeasure on wrong LayoutManager.
• Attempt to call InvalidateArrange on wrong LayoutManager.

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/aed201449d6c0016. Report an issue: GitHub.